1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates a reel on which a recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes, such as magnetic tapes and the like, are used as external recording media of computers and the like. Little space is required for storage of the recording tape, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used which rotatably accommodates, within a case, a single reel on which such a recording tape is wound. (See Japanese Patent Application Laid-Open No. 63-251983 and Japanese Patent No. 3187022, for example.)
The reel, which forms the recording tape cartridge, has a resin-formed reel hub at an axial central portion thereof. The reel hub is formed in a tubular shape having a floor. A recording tape is wound on an outer peripheral portion of the reel hub. Flanges are provided at both axial end portions of the reel hub. One flange is provided integrally with the reel hub and forms a main portion of the reel. The other flange is formed as a separate component and is attached firmly to the reel hub by welding or the like.
An annular reel gear is provided on an outer surface of the floor portion of the reel hub, along an outer circumference portion of the floor portion. The reel gear is exposed to the exterior from a gear opening of the case. The reel gear meshes with the driving gear, which is formed at a rotating shaft of the drive device. When the rotating shaft is rotated while the reel gear is meshed with the driving gear, the recording tape is pulled out of the case or taken up onto the reel in the case.
A disc-shaped metal plate, made of a magnetic material, is attached firmly to the outer surface of the reel hub at an inner side of the reel gear. In the state in which the reel gear is meshed with the driving gear, the metal plate is magnetically attracted and held in a non-contact manner by a magnet provided at the rotating shaft. The attracting force keeps the reel gear and the driving gear being meshed with each other.
Known methods of firmly attaching such metal plate to the reel hub include insert molding, and welding by caulking. These methods will be described referring to drawings.
As shown in FIG. 14, at a reel 200, a metal plate 206 is firmly attached by insert molding to a floor portion 202A of a reel hub 202 at an inner side of a reel gear 204. A flange 208 extends integrally from one axial direction end portion of the reel hub 202. A through hole 210 is provided at an axial central portion of the metal plate 206. The through hole 210 is of a so-called socket-and-spigot joint shape having a large-diameter portion 210A provided at the axial end portion opposite to the floor portion 202A. Further, three through holes 212 (only one of them is illustrated) are formed in the metal plate 206 at the radial direction outer side portions of the through holes 210 along a circumference coaxially with the through holes 210. Each through hole 212 is of a socket-and-spigot joint shape having a large-diameter portion 212A.
In the reel 200, gate portions G are provided in the metal plate 206 at an inner side of the through holes 210. At the time of resin molding, a resin material, which is a molding material, is introduced through the gate portions G. In the reel 200, by pouring the resin material through the gate portions G into a mold in which the metal plate has been inserted, the reel hub 202 and the flange 208 can be formed integrally and the metal plate 206 is attached firmly to the reel 200.
In the reel 220 shown in FIG. 15, the metal plate 224 is welded by caulking to the floor portion 222A of the reel hub 222 at an inner side of the reel gear 204. A through hole 226 is provided at an axial central portion of the floor portion 222A of the reel hub 222. A braking member, which prevents rotation of the reel when the recording tape cartridge 10 is not in use, is operated from outside via the through hole 226. A plurality of caulking projections 228 is provided protruding from the outer surface of the floor portion 222A. A through hole 230 corresponding to the through hole 226, and a plurality of through holes 232 corresponding to the caulking projections 228 are formed in the metal plate 224. In the reel 220, after the reel hub 222, the flange 208 and the like are integrally formed, the caulking projections 228 are inserted in the through holes 230 of the metal plate 224. By the caulking projections 228 being caulked, the metal plate 224 is attached firmly to the floor portion 222A.
In the reel 220, the gate portions G are provided in the outer surface of the floor portion 222A between the through hole 226 and the reel gear 204. By the resin material being introduced through the gate portions G to fill the mold, the reel hub 202 and the flange 208 are integrally formed. In this way, the metal plate 224 is attached firmly to the outer surface of the floor portion 222A so that the gate portions G are covered by the metal plate 224. Although not illustrated, such a structure is also known that each through hole 232 has a large diameter portion into which the resin material enters after the caulking so that the caulking projections 228 does not project out further than the metal plate 224.
However, the structure shown in FIG. 14 has the following drawbacks. First, it is necessary to provide a relatively large through hole 210 at the axial central portion of the metal plate 206 in order to provide the gate portions G. As a result, the area of the metal plate 206 for being attracted by the magnet is made small. Second, because the gate portions G are provided utilizing the through hole 210 that passes through the metal plate 206, in the case in which, for example, a plurality of gate portions G is to be provided, it is necessary to position the metal plate 206 in a direction in which the metal plate rotates using a dedicated equipment. Third, in the case in which, for example, the gate portions G are provided at places which are offset from the axial central portion, it is necessary to position the metal plate 206 within the mold. Further, the setting for resin molding becomes complex and the metal plate 206 may often be defectively attached.
In the structure shown in FIG. 15, because the metal plate 224 is welded by caulking after the reel hub 222 is molded, inclination of the surface of the metal plate 224 often becomes inconsistent depending on conditions of caulking, and thus it is difficult to obtain surface profile accuracy of the metal plate 224. In particular, if the gate scar after the molding of the reel hub 222 remain projecting, the metal plate 224 which the gate scar is to abut often inclined. As a result, the surface profile accuracy of the metal plate 224 often cannot be kept within the tolerance.